1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly, to color filters in a liquid crystal display device and a method of fabricating thereof.
2. Description of the Related Art
A cathode ray tube (CRT) monitor has mainly been used for displaying information in TV and computer so far. The CRT has high image quality and brightness. However, as an image screen grows larger, the depth of the CRT monitor becomes so big that the monitor occupies a very large volume. In addition, the weight of the CRT display has always been a problem in portable devices.
To address the problems above, flat panel display devices, such as liquid crystal displays, plasma display panels, organic electro luminescence displays, light emitting diodes and, field emission displays, have been used instead of a CRT monitor. Among these flat panel display devices, the liquid crystal display (LCD) device is used as a monitor of a notebook PC or of a desktop PC because the LCD has low power consumption. Color filters and a manufacturing thereof for a related art LCD device having all kinds of display applications will be described in detail with reference to FIGS. 1, 2A and 2B.
FIG. 1 is a view showing a cross-section of a related art general LCD device. As shown in FIG. 1, the LCD device includes a lower substrate 10, an upper substrate 20, and a liquid crystal layer 15 formed in between the upper and lower substrates 10 and 20. A thin film transistor T and a pixel electrode 7 are formed on the lower substrate 10. The thin film transistor T includes: a gate electrode 1 to which a scan signal is applied; a semiconductor layer 3 for transmitting a data signal corresponding to the scan signal; a gate insulating layer 2 for isolating the semiconductor layer 3 and the gate electrode 1 electrically; a source electrode 4 formed on an upper part of the semiconductor layer 3 for applying the data signal; and a drain electrode 5 applying the data signal to the pixel electrode 7. The semiconductor layer 3 comprises an active layer 3a formed by depositing amorphous silicon (a-Si), and an n+ doped ohmic contact layer 3b on both upper sides of the active layer 3a. A passivation layer 6 and the pixel electrode 7 are formed on the thin film transistor T, and a first alignment layer 4a formed for aligning liquid crystal molecules is formed on an upper part of the pixel electrode 7. The pixel electrode 7 is made by a transparent conductor, such as indium tin oxide (ITO) or indium zinc oxide (IZO), so that the light can be transmitted through the pixel electrode.
A black matrix 12 is formed on the upper substrate 20 for preventing the light from leaking between pixels, and color filters 11 of Red R, Green G, and Blue B for realizing actual colors are formed on the black matrix 12. A flattening layer (not shown) can be additionally formed on the color filter 11 for flattening the color filter and for improving an adhesive bond to a common electrode 13 subsequently formed on the color filter. The common electrode 13 is for applying voltage to the liquid crystal layer 15. A second alignment layer 4b for aligning the liquid crystal molecules is formed on the common electrode 13. A transparent conductor, such as ITO or IZO, is used as the common electrode 13 such that the light can be transmitted through the common electrode.
The LCD device is made by repeating processes, such as thin film deposition, and photolithography and etching processes, for each color used in the LCD device. Fabrication methods for color filters include: the stain method, pigment disperse method, and an electrophoresis deposition method. These three kinds of methods fabricate red, green, and blue primary color filters through three or more processes for each color of color filter.
The stain method includes processes for imparting photo-sensitivity to stainable polymer material, forming stain-subjected pattern, and staining the pattern with respective colors. In the color filter fabrication method of the stain method, a process of passing a stainable photosensitive film through the stain pattern is repeated for the respective R, G and B colors. Subsequently, the next step is forming a top coat layer.
The electrophoresis deposition method includes steps of forming electrophoresis deposition layers by extracting respective colors by electrophoresis. However, the process for forming the electrophoresis deposition layers on a transparent conductive layer has to be repeated three times to achieve each of the respective colors. Therefore, the fabrication process for the color filter takes a lot of time and has complicated process operations.
The pigment disperse method includes the steps of making a colored resist by dispersing the pigment on a resin and applying respective colored patterns. The steps of applying the colored resist and forming the colored pattern are repeated to achieve each of the respective red, green and blue colors, and therefore, fabrication time is increased and cost is increased. Also, to form the respective R, G and B color filters, the colored resist is deposited across the entire substrate and portions except the necessary portion should be removed. Since only ⅓ of the entire resist sheet is needed, ⅔ of the entire resist sheet should be removed, and therefore, the resist is heavily wasted.
An ink jet method for forming the color filters precisely were the color filters should be positioned on an LCD device has been suggested for solving the problems in the above methods. The ink jet method Red R, Green G and Blue B colored inks through an injection nozzle of an ink jet device onto to the lower substrate. The ink jet method can be used in the thin film transistor on color filter LCD device structure to preventing color filter mis-alignment and to improve the aperture rate.
FIGS. 2A and 2B are views showing a fabrication method for a color filter of an LCD device in the ink jet method of the related art. As shown in FIG. 2A, the gate electrode 51, the gate insulating layer 52 and the semiconductor layer 53 of a thin film transistor are formed on the transparent lower substrate 50. Source and drain electrodes 54 and 55, which are separated from each other with a predetermined gap, are formed on the semiconductor layer 53 using photolithography. In addition, a photoresist is patterned to form an ink separating wall 56. A passivation layer 57 is then formed on the upper part of the wall 56 to protect the thin film transistor T.
As shown in FIG. 2B, the respective R, G and B colored inks 60a are injected through the injection nozzle 60 into the pixels using the ink separating wall 56. Subsequently, the colored inks 60a solidify to form a color filter 59 in each respective pixel 59. Accordingly, the waste of ink can be prevented since it is precisely positioned. However, the color filters for each color all are positioned in a step separate from a step of positioning all of the color filters of another color. Therefore, the process is complex since subsequent color filters of one color have to be positioned amongst other already positioned color filters of another color.